1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of Related Art
Conventionally, there have been known electrographic type image forming apparatuses each of which develops, with toners, electrostatic latent images formed on photoreceptors to form toner images, transfers the formed toner images onto a sheet, heats and fixes the transferred toner images and thereby form an image on the sheet.
In an electrographic type image forming apparatus, when forming an image on continuous paper (for example, a roll of paper), if the apparatus stops conveying the sheet at the start of image formation (when a fixing temperature increases) and at the end of image formation (when the fixing temperature decreases), a certain part of the continuous paper is heated, and thus, burn and deformation are respectively generated on normal paper and artificial paper.
Thus, by conveying the continuous paper at a low speed until the fixing temperature is raised to a predetermined temperature at the start of image formation, the damage to the continuous paper is reduced while reducing waste by shortening the portion having no image formed, that is, the portion to be wasted. However, in order to decrease the fixing temperature at the end of image formation to a temperature not damaging the continuous paper, a longer time is required compared to the above raising of fixing temperature. Thus, even if the continuous paper is conveyed at a low speed, the portion having no image formed is longer compared to the length thereof when raising the fixing temperature, and more portion is wasted.
Thus, there have been disclosed techniques for controlling a heating roller not to contact the continuous paper which is stopped being conveyed by moving away one of heating rollers disposed on upper surface side and lower surface side of the continuous paper (for example, see Japanese Patent Application Laid Open Publication No. H2-103076). According to the technique described in Japanese Patent Application Laid Open Publication No. H2-103076, the burn of normal paper and deformation of artificial paper can be prevented by securing a sufficient distance to separate the heating roller away.
However, the separation distance of the heating roller is normally limited to approximately 2 to 3 mm in order to prevent the apparatus from getting larger, and thus, this degree of separation amount was insufficient to prevent the influence on sheets (especially, to prevent deformation of artificial paper).